fix(publicip): rework run loop and fix restarts

- Clearing IP data on VPN disconnection clears file
- More efficient partial updates
- Fix loop exit
- Validate settings before updating

internal/publicip/update.go

@@ -0,0 +1,82 @@
+package publicip
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/qdm12/gluetun/internal/configuration/settings"
+)
+
+func (l *Loop) update(partialUpdate settings.PublicIP,
+	lastTick time.Time, timer *time.Timer, timerIsReadyToReset bool) (
+	newTimerIsReadyToReset bool, err error) {
+	newTimerIsReadyToReset = timerIsReadyToReset
+	// No need to lock the mutex since it can only be written
+	// in the code below in this goroutine.
+	updatedSettings, err := l.settings.UpdateWith(partialUpdate)
+	if err != nil {
+		return newTimerIsReadyToReset, err
+	}
+
+	if *l.settings.Period != *updatedSettings.Period {
+		newTimerIsReadyToReset = l.updateTimer(*updatedSettings.Period, lastTick,
+			timer, timerIsReadyToReset)
+	}
+
+	if *l.settings.IPFilepath != *updatedSettings.IPFilepath {
+		switch {
+		case *l.settings.IPFilepath == "":
+			err = persistPublicIP(*updatedSettings.IPFilepath,
+				l.ipData.IP.String(), l.puid, l.pgid)
+			if err != nil {
+				return newTimerIsReadyToReset, fmt.Errorf("persisting ip data: %w", err)
+			}
+		case *updatedSettings.IPFilepath == "":
+			err = os.Remove(*l.settings.IPFilepath)
+			if err != nil {
+				return newTimerIsReadyToReset, fmt.Errorf("removing ip data file path: %w", err)
+			}
+		default:
+			err = os.Rename(*l.settings.IPFilepath, *updatedSettings.IPFilepath)
+			if err != nil {
+				return newTimerIsReadyToReset, fmt.Errorf("renaming ip data file path: %w", err)
+			}
+		}
+	}
+
+	l.settingsMutex.Lock()
+	l.settings = updatedSettings
+	l.settingsMutex.Unlock()
+
+	return newTimerIsReadyToReset, nil
+}
+
+func (l *Loop) updateTimer(period time.Duration, lastFetch time.Time,
+	timer *time.Timer, timerIsReadyToReset bool) (newTimerIsReadyToReset bool) {
+	disableTimer := period == 0
+	if disableTimer {
+		if !timer.Stop() {
+			<-timer.C
+		}
+		return true
+	}
+
+	if !timerIsReadyToReset {
+		if !timer.Stop() {
+			<-timer.C
+		}
+	}
+
+	var waited time.Duration
+	if lastFetch.UnixNano() > 0 {
+		waited = l.timeNow().Sub(lastFetch)
+	}
+	leftToWait := period - waited
+	if leftToWait <= 0 {
+		leftToWait = time.Nanosecond
+	}
+
+	timer.Reset(leftToWait)
+	return false
+}